<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>clear</title>
<style type="text/css">
header {
	background: #abcdef;
}
header::after {
	display: block;
	content: "";
	clear: both;
}
header > article {
	float: left;
	width: 40%;
	height: 30px;
	background: #f00;
}
header > aside {
	float: right;
	width: 40%;
	height: 50px;
	background: #ff0;
}
</style>
</head>
<body>
<header>
	<article></article>
	<aside></aside>
</header>
</body>
</html>